In general, a heater is a heat transfer means that permits current to flow into a conductor to dissipate heat from the conductor so as to heat fluid such as air or water. Such a heater is applied to a variety of kinds of home electronic appliance. For example, a heater used to heat water to boil it requires the physical properties such as corrosion resistance, wear resistance, and the like to prevent corrosion of the heater, and a heater used to heat air requires the outer surface of a heater rod to be coated with ceramic to improve the mechanical and chemical properties thereof to prevent oxidation of the heater in the air.
As such, as a representative example to which the heater is applied, a home electronic appliance, i.e., a washing machine employs a heater to supply hot water to increase the washability of clothes. In this case, since the washing machine uses a synthetic detergent containing various kinds of surfactants or the like, the heater rod of the heater is corroded and damaged or has scales formed on the surface thereof, resulting in occurrence of problems in that heat transfer is not performed smoothly to water to be used.
Such a conventional heater entails the above-mentioned problems, and in case of the heater for heating water to boil it as a solution to these problems, Korean Patent Laid-Out Publication No. 10-2003-37786 discloses a heater of a drum type washing machine which includes a hot wire disposed at the center thereof, a magnesium oxide layer configured to surround the outer circumference of the hot wire, and a stainless steel alloy layer configured to surround the outer circumference of the magnesium oxide layer, and a hard coating layer configured to surround the outer circumference of the stainless steel alloy layer. Such a heater is surface-treated to improve the physical properties including corrosion resistance, wear resistance, and the like. In addition, Korean Patent Laid-Out Publication No. 10-2000-2187 discloses an electric heater of a drum type washing machine in which an arrangement structure of the electric heater is modified within the washing machine to minimize the amount of washing water used and reduce the amount of power used. Further, Korean Utility Model Registration No. 20-393630 discloses a heater having a scale deposition preventive function in which the heater is coated with an inorganic-ceramic paint consisting of an inorganic binder solution prepared by adding a silica sol to a silane compound and stirring the mixture, a functional additive, a silicon oil polymer, and a water-soluble fluorine compound to prevent the disposition of scales on the heater. A variety of kinds of heaters as mentioned above have been developed and patent applications thereof have been filed. However, the heaters of these patents are suitable for heating water, but not for being used in the air. Specifically, in the case where fluorine resin is contained in a ceramic composition coated on the surface of a heater like the heater disclosed in Korean Utility Model Registration No. 20-393630, when the heater is heated to more than 260° C. in the air, the fluorine resin is decomposed due to low heat resistance, leading to a risk of damaging the coating film.
In addition, in case of the heater for heating air to dry the laundry, Korean Patent Laid-Out Publication No. 10-2005-66291 discloses a dry heater of a washing machine in which an insulator is configured to support a coil for generating heat. Such an electric heater, however, is a device in which electric current is supplied to the coil to generate heat from the coil and air receives heat from the heater while passing through the heater to produce high temperature and dry hot air. For this reason, the electric heater is technically limited to an arrangement structure of a heater to increase the dry efficiency.
The above conventional heaters, which have been used in the washing machine, have been developed so as to be suitable for their purpose in water or air. Also, heaters having the physical properties suited to the combined use in water and air have not been developed yet. As a solution to the above-mentioned problems, Korean Patent Laid-Out Publication No. 10-2005-97276 discloses a drum type washing machine with a single integrated heater in which a heater performing a function of doing laundering while boiling the laundry and a heater performing a function of drying the laundry are integrated into a single unit to simultaneously perform the both functions, thereby reducing the number of parts installed in the washing machine and the manufacturing cost, simplifying the structure of the washing machine, and saving the amount of washing water. As shown in FIG. 1, the drum type washing machine includes a cabinet 100 having a laundry inlet hole 12 formed at the front side thereof and a door 50 formed at the inlet hole 12 for opening and closing the inlet hole 12, a tub 20 mounted in the cabinet 10 for storing washing water therein, a driving motor 30 mounted below a bottom of the tub 10 for generating a driving force, a drum 40 mounted in the tub 20 and configured to be rotated by the driving force applied thereto from the driving motor 30, and a drying device 60 mounted at the inner upper portion of the cabinet 10 for circulating air in the interior of the drum 40 and removing moisture contained in the circulated air to dry a laundry received in the drum. In addition, the drum type washing machine further includes a heater 66 mounted in the drying device 60 to generate heat, and a water supply means 70 for supplying washing water to the inside of the drying device 60. Such a drum type washing machine has been developed and a patent application thereof has been filed. However, the integrated heater of the drum type washing machine is characterized in only a structure for mounting the integrated heater. Besides, since a material has not been developed which can satisfy the physical properties of the heater required to heat the heater in water or air, there is a limitation in its application.